In high speed data processing systems, magnetic recording has been employed for large memory capacity requirements. Data is read from and written onto the magnetic recordings using magnetic transducers commonly called magnetic heads which are positioned adjacent to the magnetic recording medium. The requirements for higher data density on the medium have imposed a requirement to read and write more data on narrow tracks formed on the media by the magnetic heads. In order to achieve maximum efficiency from the transducers, the magnetic head elements, the transducers are formed from thin films of a magnetic material. The sensing elements must have a pole tip height dimension, commonly called throat height for thin film inductive heads, or element height in the case of a magneto-resistive read element, which must be maintained within a certain limited tolerance for generating a maximum amount of electrical signals from a given head element.
A method of producing a required dimension for the transducer element includes a lapping stage in which an abrasive grinding surface accurately grinds the transducer element to a desired dimension. Suitable techniques for controlling the transducer dimension during the lapping operation are described in U.S. Pat. Nos. 3,821,815, 4,676,986 and 4,689,877, all assigned to the assignee of the present invention. In these patents, a technique is employed for measuring the resistance of an element located on the substrate containing the transducers being lapped to a final dimension. A resistance element is lapped along one dimension to the same extent as the required transducer dimension. The resistance of the element at any given time indicates the amount of material that has been removed from the element and, hence, the resistance is an indication of the final required dimension of the transducer being lapped. Apparatus is also described wherein a plurality of transducers along a row are lapped by controlling the leveling of the row by having lapping control elements at both ends of the row of transducers. Other methods of controlling the lapping of a plurality of transducers includes those wherein electrical lapping guide elements are deposited together with as-lapped guide elements. Reference is made to the IBM Technical Disclosure Bulletin publication at Volume 23, No. 4, September 1980, at Page 1631, and to the article at Volume 18, No. 11, April 1976, at Pages 3782-3. In these publications, a comparison factor for determining the final element height of the transducer using lapping guide elements provides a test element, the as-lapped guide element, that is deposited having the nominal element dimension of a finished transducer. This test element, deposited at the same time that the transducer element is deposited, permits determination of the stripe height of the functional elements with accuracy and without concern for the resistivity, thickness of the films, or the effective path length of the lapping guide element. However, great pains had to be taken using precision optical equipment, for instance, in order to precisely measure the dimensions of this test element. The inaccuracies in the final transducer dimension, especially when it is used alone, are not acceptable for the requirements of the data densities required of the present day transducers.
The present invention, therefore, provides for an improved electrical lapping guide useful, for instance, in one of the systems described above to control the lapping process such that the final element dimension of thin film magnetic heads can be more accurately determined while still using batch processing techniques.